Electrochemical device including a channel of an organic material, a gate electrode, and an electrolyte therebetween

ABSTRACT

Methods of producing electrochemical transistor devices are provided, wherein a solidified electrolyte is arranged in direct contact with at least a portion of an organic material having the ability to electrochemically altering its electrical conductivity through change of redox state thereof, such that a current between a source contact and a drain contact of the transistor is controllable by a voltage applied to a gate electrode. A electrochemical transistor device is also provided, wherein an ion isolative material is provided between a solidified electrolyte and an organic material having the ability to electrochemically altering its redox state, such that a transistor channel of said transistor is defined thereby.

This is a Continuation of U.S. patent application Ser. No. 10/819,306,filed Apr. 7, 2004, now U.S. Pat. No. 7,012,306 which in turn is aContinuation-in-Part of U.S. patent application Ser. No. 10/091,419filed Mar. 7, 2002 now U.S. Pat. No. 6,806,511 claiming the benefitunder 35 U.S.C. § 119(a)-(d) of Swedish Application No. 0100748-3, filedMar. 7, 2001 and under 35 U.S.C. § 119(e) of U.S. provisionalapplication No. 60/276,218, filed Mar. 16, 2001.

FIELD OF THE INVENTION

The present invention relates to electrochemical devices, in particularto printable, electrochemical transistor devices based on conductingorganic materials.

BACKGROUND OF THE INVENTION

Semiconducting and conducting organic materials, both polymers andmolecules, have successfully been included in a large range ofelectronic devices, e g electrochemical devices, for instance as dynamiccolorants in smart windows and in polymer batteries. Reversible dopingand de-doping involving mobile ions switches the material betweendifferent redox states.

Use has been made of semiconducting polymers for the realization offield effect transistor (FET) devices. The transistor channel of thesedevices comprises the semiconducting polymer in question, and theirfunction is based on changes in charge carrier characteristics in thesemiconducting polymer, caused by an externally applied electric field.In such transistors, the polymer is used as a traditional semiconductor,in that the electric field merely redistributes charges within thepolymer material. One such transistor has been realized, which isadapted for miniaturization and can be used for the production ofintegrated circuits consisting entirely of polymer material (PCTpublication WO99/10939). A stack of sandwiched layers is described, witheither a top-gate or a bottom-gate structure. A transistor device with asimilar architecture, also using a polymer as semiconducting material inthe channel of the transistor, is described in the European patentapplication EP1041653.

Another type of transistor device based on organic materials utilizeselectrochemical redox reactions in the organic material. These devicescomprise an electrolyte and a conducting polymer that can be switchedbetween an oxidized and a reduced state. One of these oxidation statesthen corresponds to low, preferably zero, conductivity in the material,whereas the other oxidation state corresponds to a high conductivityrelative to the first state. Electrochemical transistor devices havebeen used as sensors, e g for detection of oxidant in a solution (see,for review, Baughman and Shacklette, Proceedings of the SixthEurophysics Industrial Workshop (1990), p 47-61). Furthermore, atransistor of the electrochemical type is reported in Rani et al, JSolid State Electrochem (1998.), vol 2, p 99-101. The gate electrodearchitecture in this prior art transistor is shown in FIG. 1 of thisreference.

Problems with electrochemical transistor devices of the prior artinclude the fact that they are difficult and expensive to manufacture.In particular, no electrochemical transistor devices have been disclosedwhich are capable of being mass-produced. Furthermore, the practical useof prior art electrochemical transistor devices has been hampered bytheir comparatively high power consumption. Furthermore, materials usedin prior art devices suffer from a lack of environmental friendliness,processability and economic production possibilities. There is thereforea need for new and improved electrochemical transistor devices.

SUMMARY OF THE INVENTION

One of the objects of the present invention is then to meet this demand,by developing the art of electrochemical transistor devices, and byproviding a device with handling, production, disposal and othercharacteristics superior to those of the prior art.

Another object of the present invention is to provide an electrochemicaltransistor device which can be deposited on a large range of differentrigid or flexible substrates by conventional printing methods.

Yet another object of the present invention is to provide anenvironmentally safe electrochemical transistor device, so that thedisposal of the device, along with any support onto which it has beendeposited, doesn't give rise to handling problems, and so that no safetyrestrictions have to be imposed on the use of the device.

Still another object of the present invention is to make possible newapplications of conducting organic materials, using several differentproperties of such materials in combination.

A further object of the invention is to provide processes for theproduction of such devices, which processes utilize conventionalprinting methods or other deposition techniques that are well known,relatively inexpensive and easily scaled up.

The aforementioned objects are met by an electrochemical transistordevice as defined in the independent claims. Specific embodiments of theinvention are defined in the dependent claims. In addition, the presentinvention has other advantages and features apparent from the detaileddescription below.

Thus, an electrochemical transistor device is provided that comprises:

-   -   a source contact,    -   a drain contact,    -   an electrochemically active element arranged between, and in        direct electrical contact with, the source and drain contacts,        which electrochemically active element comprises a transistor        channel and is of a material comprising an organic material        having the ability of electrochemically altering its electrical        conductivity through change of redox state thereof,    -   at least one gate electrode that is separated from the        electrochemically active element, and    -   solidified electrolyte in direct electrical contact with the        electrochemically active element, through a transistor channel        interface having a spatial extension, and with the at least one        gate electrode,        wherein the transistor channel is defined by the spatial        extension of said transistor channel interface, such that flow        of electrons between source contact and drain contact is        controllable by means of a voltage applied to said gate        electrode(s).

The electrochemical transistor device according to the invention allowsfor control of electron flow between source and drain contacts in thatthe conductivity of the transistor channel of the electrochemicallyactive element can be modified, through altering of the redox state ofthe organic material therein. To provide for the necessaryelectrochemical reactions, whereby the conductivity in the transistorchannel is changed, solidified electrolyte is arranged so that it is indirect electrical contact with both the transistor channel and the gateelectrode(s). The electrochemical reaction is thus achieved byapplication of a voltage to the gate electrode(s), which generates anelectric field in the electrolyte. In the contact area betweenelectrolyte and electrochemically active element (i.e. at the transistorchannel), electrochemical redox reactions take place, which change theconductivity of the organic material in the transistor channel. Eitherthe organic material in the transistor channel is modified from aconducting state to a non-conducting state as a result of said redoxreactions, or it is modified from a non-conducting to a conductingstate, depending on the particular organic material used in theelectrochemically active element.

A general advantage with the transistors according to the presentinvention is that they are capable of modulating very high currents andvoltages. Voltages up to 70 V and currents up to 5 mA have beenmodulated without excessive device degradation. In fact, theelectrochemically active element is experienced to withstandfield-strengths reaching 1 MV/m. This fact makes the transistors veryversatile for use in a number of high effect applications. For example,the transistor can be used for controlling light emitting diodes(LED:s), LED displays, liquid crystal displays, e-INK® displays etc.

In a sense, the transistor channel operates as a resistor that isswitchable between low and high resistances. The absolute resistancevalues depend on the organic material used and on the structural designof the transistor channel, and the extreme values are obviously zero andinfinite, respectively.

The transistor channel is restricted to a portion of theelectrochemically active element, such that portions of theelectrochemically active element are electrically conductive regardlessof the redox state in the transistor channel. Thereby the actual size,position, and design of the transistor channel is determined by theelectrolyte. This is advantageous in that the electrochemically activeelement may be deposited with a low degree of precision, and only theelectrolyte needs to be applied with a high degree of precision.

The position of the electrochemical transistor in a circuit may becritical for proper operation. This is especially true in case organicmaterial is used as conductors in the circuitry, since the internalresistance in such conductors may affect the behavior of the circuitry.However, positioning of the electrochemical transistor in accordancewith the present invention is readily and accurately provided for byaccurate positioning of the electrolyte. Consequently, theelectrochemically active element need not have a very accurate positionand it is therefore possible to apply the electrochemically activeelement with a relatively low spatial accuracy. This also facilitatestuning of the transistor characteristics by selecting an appropriateshape for the electrolyte interface. The transistor channel may, forexample, be given a triangular shape or a saw-toothed shape.

However, in one embodiment, the transistor channel should occupy theentire cross-section of the connection between the drain and sourcecontacts in order to limit current leakage between the respectivecontacts.

Based on the electrochemical transistor described above it is possibleto arrange semifinished circuitries that carry a number of potentialtransistors. Such a semifinished product can provide for a number ofdifferent “potential” circuitries, and a desired circuitry layout may beselected from the potential circuitries by activating the relevanttransistor(-s). Activation is carried out by applying electrolyte thatinterface the relevant electrochemically active element(-s) whileleaving the remaining active elements open.

The electrolyte may be applied selectively on the device, using forexample a printing technique. An alternative approach, however, is toapply a layer of ion isolative material on top of the electrochemicallyactive element, except for an open area where the transistor interfaceis to be arranged. Thereafter the electrolyte may be deposited with alow degree of precision, since the transistor interface, and thus thetransistor channel, will anyway be defined as the open area in the layerof ion isolative material. The layer of ion isolative material may infact be arranged to cover the entire device, except for areas whereelectrolyte is suppose to have direct electrical contact with the device(e.g. the gate electrodes).

Furthermore, the electrolyte may be arranged as one homogenous element,or as a number of separate elements not having ionic contact with eachother. According to one embodiment, a continuous or interrupted layer ofsaid solidified electrolyte covers the transistor channel and covers atleast partially said gate electrode(s).

When a voltage is applied to the gate electrode(s), a redox reactionoccurs in the transistor channel. This redox reaction is located to thearea of the electrochemically active material that is covered withelectrolyte, but also tends to migrate somewhat outside that area.Hence, the transistor channel is defined by the transistor interface butnot necessarily confined to that very area only. The migration is moresevere in case the electrochemically active element is formed out of amaterial that tends to conduct ions to some extent, such as PEDOT:PSS.

However, migration of the redox reaction outside the area that is incontact with electrolyte may be disadvantageous since it tends to slowdown the switching of the transistor. One reason for this is that redoxreactions in material that is not in close contact with the electrolyteis typically slow to reverse. Therefore, according to one embodiment, a“stopping material” is arranged that delimit the transistor channel fromthe surrounding electrochemically active element/material.

The stopping material may be a material that is electrically conductivebut ionically non-conductive, or it may be a material that iselectrochemically non-active at the voltages used. Alternatively it maybe a material or material combination that has a differentelectrochemical potential than the electrochemically active materialresiding in the transistor channel. Materials combining some or all ofthese effects are also contemplated. The stopping material may actuallybe the same material as in the transistor channel but slightly modifiedto render it less ion-conducting, electrochemically non-active, or toalter its electrochemical potential. These effects or combinations ofthem can be exploited using any known method.

The stopping material may be arranged to delimit the transistor channeltowards the source contact, the drain F contact, and/or towards gateelectrode(s).

The architecture of the electrochemical transistor device according tothe invention is advantageous in that it makes possible the realizationof a layered transistor device with only a few layers, having forexample one patterned layer of material comprising a conducting organicmaterial, which layer comprises source and drain contacts and gateelectrode(s), as well as the electrochemically active element. Thesource and drain contacts and the electrochemically active element arethen preferably formed by one continuous piece of said material. Thesource and drain contacts could alternatively be formed from anotherelectrically conducting material in direct electrical contact with theelectrochemically active element. The gate electrode(s) may also be ofanother electrically conducting material. However, a particularadvantage in the electrochemical transistor is that the gateelectrode(s), the source and drain contacts, and the transistor channelcan be formed out of one and the same organic material. Furthermore,this organic material can be used not only for the transistor as such.Rather, the same organic material, and hence also the same manufacturingstep (e.g. a printing step) can provide for connector strips andpossibly also other type of electrical components. Resistors is oneexample of such a component, which may be formed out of a organicmaterial conductor path having a length and cross-section that providefor the desired resistance.

Thus, according to one embodiment, at least one of the source and draincontacts and the gate electrode(s) is formed from the same material asthe electrochemically active element. Obviously, in yet one embodiment,all of the source and drain contacts and the gate electrode(s) areformed from the same material as the electrochemically active element.

In case source and/or drain contacts are formed out of an organicmaterial, there might not exist any distinct delimiter between thesecomponents and the electrochemically active element. In some embodimentsall these three components are actually formed out of a continuous pieceof the same material. However, distinction between these components arenot necessary for the purpose of the present invention. In someapplications, the source and/or drain contacts are formed out of anorganic material and are interconnected with other types of materials,e.g. metal stripes forming electrical conductors that interconnects thetransistor with additional components. However, such conductors etc.need not form part of the transistor as such. When reference is made toa transistor, only the parts that is needed for proper operation of thedevice is intended. In other words, for example, a transistor havingsource, drain, gate, and electrochemically active material formed out ofan organic material may very well be interconnected with metalconductors.

In a preferred embodiment, the source and drain contacts and gateelectrode(s), as well as the active element, are all arranged to lie ina common plane, further simplifying production of the device by ordinaryprinting methods. Thus, the electrochemical device according to thisembodiment of the invention uses a lateral device architecture. A layerof solidified electrolyte can advantageously be deposited so that itcovers, at least partly, the gate electrode(s) as well as covering thetransistor cannel. This layer of solidified electrolyte may becontinuous or interrupted, depending partly on which of two main typesof transistor architectures is to be realized (see below). The layout ofthe interface between the electrolyte and the transistor channel, i.e.the transistor interface, will determine the shape and position of thetransistor channel.

According to an alternative embodiment, the electrochemical transistormay have a vertical structure. In such case the source and draincontacts and the electrochemically active element are arranged in onecommon plane, and solidified electrolyte and one gate electrode aresandwiched on the electrochemically active element.

In the transistor, the electrochemical reaction is driven by theexistence of a potential difference between the electrolyte and theelectrochemically active material. For many applications, it ispreferable to have an as even spread as possible of the redox reactionin the electrochemically active element. Vertical structures generallyprovide for a more evenly spread of the redox reaction. This is due tothe fact that, in a vertical structure, the potential gradient is muchsteeper in the vertical direction than in the lateral direction. This isopposed to lateral structures wherein the potential gradient typicallyis much steeper in the lateral direction. Or, in other words, the redoxreaction in the electrochemically active element grows from the gateelectrode direction of the electrochemically active element (i.e. fromthe side of the element in a lateral structure and from the top of theelement in a vertical structure). Advantages of vertical structuresfurther include a more compact design and possibly also a more rapidelectrochemical response (since the ion current in the electrolyte needonly travel vertically across the thickness of the solidifiedelectrolyte). Hence, transistors having vertical and lateral structurescan be made to have different time dependant switching characteristics.Naturally, it is possible to combine vertical and lateral transistors ina circuitry, for example in case transistors operating on differenttime-scales are desired.

As is readily appreciated by the skilled person, and in analogy toconventional field effect transistors, the electrochemical transistordevice of the invention may readily be made to function as a diodedevice through short-circuiting of the gate electrode and sourcecontact, or of the gate electrode and drain contact. One non-limitingexample of this is described in the description below. However, anyconfiguration of the electrochemical transistor device may naturally beused as a diode in this fashion.

Depending on the precise patterning of the conducting organic materialand the electrolyte, the electrochemical transistor device of theinvention can either be of a bi-stable or a dynamic type. In thebi-stable transistor embodiment, a voltage applied to the gateelectrode(s) leads to a change in conductivity in the transistor channelthat is maintained when the external circuit is broken, i e when theapplied voltage is removed. The electrochemical reactions induced by theapplied voltage can not be reversed, since the electrochemically activeelement and the gate electrode(s) are not in direct electrical contactwith each other, but separated by electrolyte. In this embodiment, thetransistor channel can be switched between non-conducting and conductingstates using only small, transient gate voltages. The bi-stabletransistor can be kept in an induced redox state for days, and, in themost preferred, ideal case, indefinitely.

Thus, the bi-stable transistor embodiment of the present inventionoffers a memory function, in that it is possible to switch it on or offusing only a short voltage pulse applied to the gate electrode. Thetransistor stays in the conducting or non-conducting redox state evenafter the applied voltage has been removed. A further advantage withsuch bi-stable transistors is that close to zero-power operation is madepossible, since the short voltage pulses applied to the gate need not belarger than a fraction of the gate voltages needed for operation of acorresponding dynamic device.

In the dynamic transistor embodiment, the change in the redox state ofthe material is reversed spontaneously upon withdrawal of the gatevoltage. This reversal is obtained through the provision of a redox sinkvolume adjacent to the transistor channel in the electrochemicallyactive element. Also, a second gate electrode is provided, and arrangedso that the two gate electrodes are positioned on either side of theelectrochemically active element, one closer to the transistor channel,and the other closer to the redox sink volume. Both gate electrodes areseparated from the electrochemically active element by electrolyte.Application of a voltage between the two gate electrodes results in theelectrochemically active element being polarized, whereby redoxreactions take place in which the organic material in the transistorchannel is reduced while the organic material in the redox sink volumeis oxidized, or vice versa. Since the transistor channel and the redoxsink volume are in direct electrical contact with each other, withdrawalof gate voltage leads to a spontaneous reversal of the redox reactions,so that the initial conductivity of the transistor channel isre-established. It is to be stressed that in contrast to electrochemicaltransistors of the prior art, dynamic transistors according to thisembodiment of the present invention revert spontaneously to the initialconductivity state without the need for a reversing bias.

The electrochemical transistor device according to the invention is alsoparticularly advantageous in that it can be easily realized on asupport, such as polymer film or paper. Thus, the different componentscan be deposited on the support by means of conventional printingtechniques such as screen printing, offset printing, gravure printing,ink-jet printing and flexographic printing, or coating techniques suchas knife coating, doctor blade coating, extrusion coating and curtaincoating, such as described in “Modern Coating and Drying Technology”(1992), eds E D Cohen and E B Gutoff, VCH Publishers Inc, New York,N.Y., USA. In those embodiments of the invention that utilize aconducting polymer as the organic material (see below for materialsspecifications), this material can also be deposited through in situpolymerization by methods such as electropolymerization,UV-polymerization, thermal polymerization and chemical polymerization.As an alternative to these additive techniques for patterning of thecomponents, it is also possible to use subtractive techniques, such aslocal destruction of material through chemical or gas etching, bymechanical means such as scratching, scoring, scraping or milling, or byany other subtractive methods known in the art. An aspect of theinvention provides such processes for the manufacture of anelectrochemical transistor device from the materials specified herein.

However, the invention is not limited to supported devices, as thecontacts and electrode(s), electrochemically active element andelectrolyte can be arranged in such a way that they support each other.An embodiment of the invention thus provides for a self-supportingdevice.

According to a preferred embodiment of the invention, theelectrochemical transistor device is encapsulated, in part or entirely,for protection of the device. The encapsulation retains any solventneeded for e g the solidified electrolyte to function, and also keepsoxygen from disturbing the electrochemical reactions in the device.Encapsulation can be achieved through liquid phase processes. Thus, aliquid phase polymer or organic monomer can be deposited on the deviceusing methods such as spray-coating, dip-coating or any of theconventional printing techniques listed above. After deposition, theencapsulant can be hardened for example by ultraviolet or infraredirradiation, by solvent evaporation, by cooling or through the use of atwo-component system, such as an epoxy glue, where the components aremixed together directly prior to deposition. Alternatively, theencapsulation is achieved through lamination of a solid film onto theelectrochemical transistor device. In preferred embodiments of theinvention, in which the components of the electrochemical transistordevice are arranged on a support, this support can function as thebottom encapsulant. In this case encapsulation is made more convenientin that only the top of the sheet needs to be covered with liquid phaseencapsulant or laminated with solid film.

The electrochemical transistor can be used in many differentapplications, and may readily be arranged as component in a circuit. Thetransistors described above typically carries one or two separate gateelectrodes in addition to the source electrode and the drain electrode.However, in circuit design it is important to have a reference point forthe potential. Or, in other words, the gate potential may not float inrelation to the drain/source potentials. Therefore, transistors havingonly one gate electrode is found particularly useful for many circuitryapplications. In these transistors, either source or drain is used asreference potential for the gate electrode thereby avoiding any floatinggate potential. It is also possible to design transistors that have twoor more gate electrodes that all are referenced to source or drain andthat thus eliminates any floating potential. Such transistors may beadvantageous for certain applications, since the gate electrodes can bearranged so as to provide a better potential gradient distribution inthe transistor channel (e.g. a more even spread and possibly higherspeed of the redox reaction in the channel).

Thus, according to one embodiment, the transistor device is arrangedsuch that flow of electrons between source contact and drain contact iscontrollable by means of a voltage applied between said gateelectrode(s) and one of the source contact and the drain contact.

In case the transistor channel is electrically conductive in its groundstate, i.e. before any redox reaction, the transistor is “normally open”and closes upon application of a gate voltage. In case the transistorchannel is electrically non-conductive (i.e. has a high resistance) inits ground state, the transistor is “normally closed” and opens uponapplication of a gate voltage. In analogy with traditional field effecttransistors, “normally open” electrochemical transistors are said tooperate in depletion mode and “normally closed” electrochemicaltransistors are said to operate in enhancement mode. An electrochemicaltransistor that is “normally closed” operates in the same manner as atraditional field effect transistor (i.e. application of a gate voltageopens the source—drain connection and provides for a source—draincurrent). Such transistors may be employed in circuits havingtraditional design.

However, as it turns out, many of the organic materials that have provenprosperous for use in the electrochemical transistor are such that theyare electrically conductive in their ground state and have a lowerelectrical conductivity in their reduced state. This class of polymersincludes, for example, PEDOT:PSS. This characteristic has implicationson the transistors in that it will conduct current between the sourceand drain electrodes as long as no voltage is applied on the gateelectrode(-s). Consequently, these electrochemical transistors are“normally open” and behave opposite to ordinary FET which transmitsvoltage between source and drain electrodes only when a voltage isapplied to the gate electrode.

Depending on the organic material(s) used in the electrochemicallyactive element, the voltage needed on the gate electrode to switch thetransistor from its “normal” state may be positive or negative. Hence,there are four different “types” of transistors, depending on theorganic materials used:

-   -   “normally open” that closes in response to a positive gate        voltage (comp. P-doped depletion mode transistors)    -   “normally open” that closes in response to a negative gate        voltage (comp. N-doped depletion mode transistors)    -   “normally closed” that opens in response to a negative gate        voltage (comp. P-doped enhancement mode transistors)    -   “normally closed” that opens in response to a positive gate        voltage (comp. N-doped enhancement mode transistors)

According to one embodiment, the organic material in the transistorchannel is such that flow of electrons between source contact and draincontact is restrained upon application of a positive voltage to the gateelectrode. According to an alternative embodiment the organic materialin the transistor channel is such that flow of electrons between sourcecontact and drain contact is promoted upon application of a positivevoltage to the gate electrode.

The electrochemical transistor described above can be used for manydifferent applications. An advantage is that the transistor can beformed out of the same material as conductors, resistors and capacitors,using the same manufacturing equipment (e.g. a printing technique). Aresistor, for example, is readily provided in the form of a resistorpath having a suitable length and cross-section. It is also possible toprovide capacitors using organic material. On example is given in thearticle “All-polymer RC filter circuits fabricated with inkjet printingtechnology”, Chen at el, Solid-State Electronics 47 (2003) 841-847.

Many basic circuits, such as inverters, AND, NAND, OR, and NORoperators, may be formed out of interconnected transistors andresistors. Hence, the present invention provides the hitherto missingpart (i.e. the transistor) for making cheap, printable, andenvironmentally friendly circuitries that can be arranged on e.g. aflexible substrate such as a piece of paper.

Thus, according to another aspect of the invention, a circuitrycomprising an electrochemical transistor as described above is provided.Obviously, the circuitry may comprise a number of equal or differentelectrochemical transistors.

In addition to one or more electrochemical transistors, the circuitrytypically comprises at least one resistor component that may be formedout of an organic material. The organic material is preferably the samematerial as is used in the transistor(s), and it may also be used forforming electrical junctions between different components in thecircuitry. The organic material may, for example, be one of PEDOT:PSS,polyaniline, and polypyrrole, or a combination thereof.

According to one embodiment, the circuitry comprises a resistor that hasa predefined electrical resistance and that is formed out of a path oforganic material having a S-shaped path pattern defining at least twoessentially parallel path portions.

A resistor may alternatively be formed as an integrated component in anelectrical junction. This can be achieved by suitable choice of length,width, and thickness of the junction. Hence, according to oneembodiment, a resistor having a predefined electrical resistance forms apassive electrical component and operated also as a junction between toother electrical components in the circuitry.

In circuit design, as stated above, it is typically important to have areference point for the potential. Therefore, according to a preferredembodiment, the gate potential is referenced to either of the source andthe drain contacts.

According to one embodiment, the transistor channel of theelectrochemical transistor comprises an organic material that iselectrically conductive in a ground state and that has a lowerelectrical conductivity in an electrochemically reduced state, andwherein, when the circuit is in operation, the gate potential is alwaysat least as high as the drain potential. This rule of thumb implicatesthat the drain potential is never higher than the gate potential, or, inother words, that the gate potential must be at least as high as thedesired drain potential. This design rule will ensure proper operationof electrochemical transistors wherein the electrochemically activematerial is electrically conductive in a ground state and has a lowerelectrical conductivity in an electrochemically reduced state.

A yet more stable design rule is to demand that the potential at thegate electrode should actually be at least as high as the potential atthe source electrode. Obviously, the potential at the source electrodeis thereby always at least as high as the potential at the drainelectrode (and typically higher). Thus, according to one embodiment, thegate potential is always at least as high as the source potential, andthe source potential is always at least as high as the drain potential.The circuitry described above may, for example, be used as an analogoperator or as a logic operator.

The above design rules are valid when using, for example, PEDOT:PSS inthe form of ORGACON™ EL350 as organic material. However, materials (evenother PEDOT:PSS formulations) having different characteristics mayrequire different design rules.

According to one embodiment, the circuitry is operative as a logicoperator that takes as input voltages in a first range corresponding toa logical zero and a second range corresponding to a logical one, andthat output voltages corresponding to said logical zero and logical onedepending on the input.

The logical operator may, for example, be one of:

-   -   a logic inverter and comprising a system of resistors which        ensures that the output voltages correspond to one of said        logical zero and said logical one,    -   a logic inverter comprising a second electrochemical transistor        that ensures that the output voltages correspond to one of said        logical zero and said logical one.    -   a logical AND, OR, NAND, or NOR operator, having wherein two        electrochemical transistors connected in series or in parallel    -   a comparator that takes a first input voltage and a second input        voltage as inputs and that outputs a voltage in a range        corresponding to a logical zero in case the first input voltage        is lower than the second input voltage, and outputting a voltage        in a range corresponding to a logical one in case the first        input voltage is higher than the second input voltage.

As an example of analog operators, one embodiment of the circuitryprovides an analogue amplifier, amplifying an input voltage andoutputting an amplified output voltage.

According to another embodiment, the circuitry is operative as aconstant current source, and the electrochemical transistor is employedto ensure that an output current is always within a prescribed currentrange provided that the load on the circuitry is within prescribed loadrange.

The invention will now be further described with reference to specificembodiments thereof and to specific materials. This detailed descriptionis intended for purposes of exemplification, not for limitation in anyway of the scope of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Schematic structure of one embodiment of a bi-stable transistoraccording to the invention, showing (A) a top view, (B) a cross-sectionalong I-I in A, and (C) a top view with a different position forapplication of V_(g).

FIG. 2. Schematic structure of a dynamic transistor according to theinvention, showing (A) a top view and (B) a cross-section along I-I inA.

FIG. 3. Schematic structure of another embodiment of a bi-stabletransistor according to the invention, showing (A) a top view and (B) across-section along I-I in A.

FIG. 4. I_(ds) vs V_(ds) characteristics at various gate voltages forexperiments carried out on a bi-stable PEDOT:PSS transistor as shown inFIG. 1. The inset shows I_(d) vs V_(g) at constant V_(ds) (V_(ds)=2.0 V)

FIG. 5. I_(ds) vs V_(ds) characteristics at various gate voltages forexperiments carried out on a dynamic transistor. The inset shows I_(d)vs V_(g) at constant V_(ds) (V_(ds)=2.0 V).

FIG. 6. I_(ds) vs V_(ds) characteristics at various gate voltages forexperiments carried out on a bi-stable polyaniline transistor as shownin FIG. 1. The polyaniline was supplied in toluene solution. (A) Generalcharacteristics. (B) Y-axis expansion of a part of the diagram shown inA.

FIG. 7. I_(ds) vs V_(ds) characteristics at various gate voltages forexperiments carried out on a bi-stable polyaniline transistor as shownin FIG. 1. The polyaniline was supplied in m-cresol solution.

FIG. 8: Illustrates a top view and a side view of a three-terminaltransistor having a vertical structure.

FIG. 9 a: Illustrates a top view and a side view of a three-terminaltransistor having a lateral structure.

FIG. 9 b: Graphs showing the response time for a transistor having alateral structure (left) and vertical structure (right).

FIG. 10: Electrochemical transistor with gate voltage referenced to thepositive terminal (right) and the negative terminal (left),respectively.

FIG. 11: Diagram illustrating the first quadrant characteristics of anelectrochemical transistor.

FIG. 12: Diagram illustrating the third quadrant characteristics of anelectrochemical transistor.

FIG. 13: Diagram from SPICE modeling the characteristics of a comparablep-mos depletion transistor.

FIG. 14. Circuitry in the form of a single-stage amplifier/switch.

FIG. 15: Diagram illustrating the Input/Output relationship for thesingle-stage amplifier/switch illustrated in FIG. 14.

FIG. 16: Circuitry in the form of a constant current source.

FIG. 17: Circuitry diagram for an inverter.

FIG. 18: Layout of the inverter circuit illustrated in FIG. 17.

FIG. 19: Diagram illustrating the Input/Output transfer function for theinverter illustrated in FIG. 17.

FIG. 20: Diagram illustrating the response for a binary input signal forthe circuit in FIG. 17.

FIG. 21. Illustrates a Single stage logical inverter circuitry.

FIG. 22: Diagram illustrating the transfer function for the single stageinverter in FIG. 21.

FIG. 23: Diagram illustrating the switching behavior for the singlestage inverter in FIG. 21, top curve relates to the input signal (leftscale) and the bottom curve relates to the output signal (right scale).

FIG. 24: Illustrates a 2-stage inverter circuitry with symmetric powersupply.

FIG. 25: Illustrates a ring oscillator circuitry.

FIG. 26: Diagram illustrating the output signal of the ring oscillatorshown in FIG. 25.

FIG. 27: Illustrates circuit diagrams of a NAND-gate (left) and aNOR-gate (right).

FIG. 28: Diagram illustrating output signals of the NAND-gate in FIG.27.

FIG. 29: Diagram illustrating the output signals of the NOR-gate in FIG.27.

FIG. 30: Circuit diagram (right) and response curve (right) for ananalogue amplifier.

FIG. 31: Circuit diagram (right) and response curve (right) for a singlestage AC-bypassed amplifier.

FIG. 32 a: Circuit diagram for a differential amplifier.

FIG. 32 b: Diagram showing the response of the differential amplifier inFIG. 32 a when driven with AC voltage.

FIG. 32 c: Diagram showing the response of the differential amplifier inFIG. 32 a when driven with DC voltage.

FIG. 33 a-b: Circuit diagram (FIG. 33 a) and response curve (FIG. 33 b)for a “high gain” amplifier.

FIG. 34 a-b: Circuit diagram (FIG. 34 a) and response curve (FIG. 34 b)for a power inverter.

FIG. 35 a-b: Circuit diagram (FIG. 35 a) and response curve (FIG. 35 b)for a “high gain” inverter.

FIG. 36 a-b: Circuit diagram (FIG. 36 a) and response curve (FIG. 36 b)for a first pixel driver.

FIG. 37 a-b: Circuit diagram (FIG. 37 a) and response curve (FIG. 37 b)for a second pixel driver.

FIG. 38 a-b: Circuit diagram (FIG. 38 a) and response curve (FIG. 38 b)for a high voltage driver.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Definitions

Bi-stable electrochemical transistor: an electrochemical transistordevice in which the transistor channel retains its redox state (andhence its conductivity characteristics) when the gate voltage isremoved.

Dynamic electrochemical transistor: an electrochemical transistor devicein which the transistor channel spontaneously returns to its initialredox state (and hence to its initial conductivity characteristics) whenthe gate voltage is removed.

Source contact: an electrical contact which provides charge carriers toa transistor channel.

Drain contact: an electrical contact which accepts charge carriers froma transistor channel.

Gate electrode: an electrical contact of which any fraction of thesurface area is in direct electrical contact with solidifiedelectrolyte, and therefore in ionic contact with the electrochemicallyactive element.

Electrochemically active element: an “electro-chemically active element”according to the present invention, is a piece of a material comprisingan organic material having a conductivity that can be electrochemicallyaltered through changing of the redox state of said organic material.The electrochemically active element is in ionic contact with at leastone gate electrode via a solidified electrolyte. The electrochemicallyactive element may furthermore be integrated with each of the source anddrain contacts individually or with both of them, being composed of thesame or different materials. The electrochemically active element in theelectrochemical transistor devices of the invention comprises atransistor channel, and may furthermore comprise a redox sink volume.

Transistor channel: the “transistor channel” of the electrochemicallyactive element establishes electrical contact between source and draincontacts.

Redox sink volume: in certain embodiments of the invention, theelectrochemically active element further comprises a “redox sinkvolume”. This is a part of the electrochemically active element adjacentto and in direct electrical contact with the transistor channel, whichcan provide or accept electrons to or from the transistor channel. Thus,any redox reactions within the transistor channel are complemented byopposing reactions within the redox sink volume.

Redox state: when reference is made to changes in the “redox state” ofthe electrochemically active element, this is intended to include caseswhere the organic material in the electrochemically active element iseither oxidized or reduced, as well as cases where there is aredistribution of charges within the electrochemically active element,so that one end (e g the transistor channel) is reduced and the otherend (e g the redox sink volume) is oxidized. In the latter case, theelectrochemically active element as a whole retains its overall redoxstate, but its redox state has nevertheless been changed according tothe definition used herein, due to the internal redistribution of chargecarriers.

Direct electrical contact: Direct physical contact (common interface)between two phases (for example electrode and electrolyte) that allowsfor the exchange of charges through the interface. Charge exchangethrough the interface can comprise transfer of electrons betweenelectrically conducting phases, transfer of ions between ionicallyconducting phases, or conversion between electronic current and ioniccurrent by means of electrochemistry at an interface between for exampleelectrode and electrolyte or electrolyte and electrochemically activeelement, or by occurrence of capacitive currents due to the charging ofthe Helmholtz layer at such an interface.

Solidified electrolyte: for the purposes of the invention, “solidifiedelectrolyte” means an electrolyte, which at the temperatures at which itis used is sufficiently rigid that particles/flakes in the bulk thereinare substantially immobilized by the high viscosity/rigidity of theelectrolyte and that it doesn't flow or leak. In the preferred case,such an electrolyte has the proper Theological properties to allow forthe ready application of this material on a support in an integral sheetor in a pattern, for example by conventional printing methods. Afterdeposition, the electrolyte formulation should solidify upon evaporationof solvent or because of a chemical cross-linking reaction, broughtabout by additional chemical reagents or by physical effect, such asirradiation by ultraviolet, infrared or microwave radiation, cooling orany other such. The solidified electrolyte preferably comprises anaqueous or organic solvent-containing gel, such as gelatin or apolymeric gel. However, solid polymeric electrolytes are alsocontemplated and fall within the scope of the present invention.Furthermore, the definition also encompasses liquid electrolytesolutions soaked into, or in any other way hosted by, an appropriatematrix material, such as a paper, a fabric or a porous polymer. In someembodiments of the invention, this material is in fact the support uponwhich the electrochemical transistor device is arranged, so that thesupport forms an integral part of the operation of the device.

Materials

Preferably, the solidified electrolyte comprises a binder. It ispreferred that this binder have gelling properties. The binder ispreferably selected from the group consisting of gelatin, a gelatinderivative, polyacrylic acid, polymethacrylic acid,poly(vinyl-pyrrolidone), polysaccharides, polyacrylamides,polyurethanes, polypropylene oxides, polyethylene oxides, poly(styrenesulphonic acid) and poly(vinyl alcohol) and salts and copolymersthereof; and may optionally be cross-linked. The solidified electrolytepreferably further comprises an ionic salt, preferably magnesiumsulphate if the binder employed is gelatin. The solidified electrolytepreferably further contains a hygroscopic salt such as magnesiumchloride to maintain the water content therein.

The organic material for use in the present invention preferablycomprises a polymer which is electrically conducting in at least oneoxidation state and optionally further comprises a polyanion compound.organic materials comprising combinations of more than one polymermaterial, such as polymer blends, or several layers of polymermaterials, wherein the different layers consist of the same polymer ordifferent polymers, are also contemplated. Conductive polymers for usein the electrochemical transistor device of the invention are preferablyselected from the group consisting of polythiophenes, polypyrroles,polyanilines, polyisothia-naphthalenes, polyphenylene vinylenes andcopolymers thereof such as described by J C Gustafsson et al in SolidState Ionics, 69, 145-152 (1994); Handbook of Oligo- and Polythiophenes,Ch 10.8, Ed D Fichou, Wiley-VCH, Weinhem (1999); by P Schottland et alin Macromolecules, 33, 7051-7061 (2000); Technology Map ConductivePolymers, SRI Consulting (1999); by M Onoda in Journal of theElectrochemical Society, 141, 338-341 (1994); by M Chandrasekar inConducting Polymers, Fundamentals and Applications, a PracticalApproach, Kluwer Academic Publishers, Boston (1999); and by A J Epsteinet al in Macromol Chem, Macromol Symp, 51, 217-234 (1991). In anespecially preferred embodiment, the organic material is a polymer orcopolymer of a 3,4-dialkoxythiophene, in which said two alkoxy groupsmay be the same or different or together represent an optionallysubstituted oxy-alkylene-oxy bridge. In the most preferred embodiment,the polymer is a polymer or copolymer of a 3,4-dialkoxythiopheneselected from the group consisting of poly(3,4-methylenedioxythiophene),poly(3,4-methylenedioxythiophene) derivatives,poly(3,4-ethylenedioxythiophene), poly(3,4-ethylenedioxythiophene)derivatives, poly(3,4-propylenedioxythiophene),poly(3,4-propylenedioxythiophene) derivatives,poly(3,4-butylene-dioxythiophene), poly(3,4-butylenedioxythiophene)derivatives, and copolymers therewith. The polyanion compound is thenpreferably poly(styrene sulphonate).

The support in some embodiments of the electrochemical transistor deviceof the present invention is preferably selected from the groupconsisting of polyethylene terephthalate; polyethylene naphthalenedicarboxylate; polyethylene; polypropylene; paper; coated paper, e.g.coated with resins, polyethylene, or polypropylene; paper laminates;paperboard; corrugated board; glass and polycarbonate.

PEDOT:PSS can, in an electrochemical cell, be switched between a highconducting state (oxidized) and a low conducting state (reduced)according to the reaction below:PEDOT ⁺ PSS ⁻ +M ⁺ +e ⁻ →PEDOT ⁰ +M ⁺ PSS ⁻

The metal ion M⁺ is supplied by the electrolyte and the electron e⁻ istransported by PEDOT. It is not only the conducting properties ofPEDOT:PSS that is changed, also the optical properties are changed.PEDOT:PSS appears transparent in the oxidized state and deep blue in thereduced state. This implies possibilities to create electrochromicdisplay elements out of the transistor, utilizing the color changes inthe transistor channel when oxidized or reduced. PEDOT:PSS is coated ona polyester carrier, ORGACON™ EL-350 used as received by AGFA-GAEVART.The PEDOT:PSS film received is in a partially oxidized state (highlyconducting state) which allows PEDOT to be further oxidized. At elevatedoxidation potential PEDOT can be oxidized to a non-reversiblenon-conducting state, which we refer to as an over-oxidized state.

Principal Device Architectures

By patterning of the organic material of the electrochemically activeelement and of the contacts, electrode(s) and electrolyte in differentways, two main types of electrochemical transistor devices can berealized. These main types, bi-stable and dynamic electrochemicaltransistor devices, will now be exemplified along with reference tofigures thereof and an outline of their working principles.

Bi-stable transistor (type 1): FIGS. 1A and 1B schematically show oneembodiment of a bi-stable transistor. The transistor comprises a sourcecontact 1, a drain contact 2 and an electrochemically active element 3,which have all been formed from a continuous piece of organic material.Both the source and drain contacts are in electrical contact with anexternal power source, which allows the application of a voltage V_(ds)between them. The transistor further comprises a gate electrode 4, whichcan be formed from the same organic material as the source and draincontacts and the electrochemically active element. The gate electrode 4is in electrical contact with an external power source, which allowsapplying a voltage V_(g) between the gate electrode and theelectrochemically active element. This can be realized by applying V_(g)between the gate 4 and the source 1 or the drain 2, or directly betweenthe gate 4 and the electrochemically active element 3. All of theseorganic material components have been deposited in one layer on asupport 6. On top of this layer, covering part of the gate electrode 4and the active element 3, is a layer of gel electrolyte 5. Furthermore,the gel electrolyte layer 5 is covered with an encapsulating layer 7 forprevention of solvent evaporation.

Working principle for the polarity of V_(g) shown in FIG. 1, and in thecase of an organic material which is conducting in its oxidized stateand non-conducting when reduced to its neutral state: when a gatevoltage V_(g) is applied between the gate electrode 4 and theelectrochemically active element 3, the gate electrode is polarizedpositive (anode), and the electrochemically active element is polarizednegative (cathode). This leads to onset of electrochemistry in theelectrochemically active element and at the gate electrode; the organicmaterial in the transistor channel is reduced at the same time as anoxidation reaction takes place at the gate electrode. The reducedmaterial in the transistor channel displays a drastically diminishedelectrical conductivity, which results in the closure of the transistorchannel and an effective reduction of the current between source anddrain for a given source-drain voltage V_(ds), i e the transistor is inan “off” mode. When the external circuit supplying voltage to the gateelectrode and the electrochemically active element is broken, theoxidation state of the transistor channel is maintained. No reversal ofthe electrochemical reactions is possible because of the interruption byelectrolyte 5 of electron flow between gate electrode 4 andelectrochemically active element 3.

Thus, the bi-stable transistor has a memory-function: It is possible toswitch on or off the transistor channel with short pulses of gatevoltage, V_(g), applied to the gate. The respective conductivity statesremain when gate voltage is removed (a zero-power device). Furtheradjustments of conduction characteristics in the electrochemicallyactive element, or resetting thereof to the initial, high conductivitymode, can be performed by applying different voltages to the gateelectrode.

As explained above in the summary, the transistor device of theinvention may easily be made to function as a diode. This is achievedfor example through a transistor device architecture as shownschematically in FIG. 1C. In comparison to the device discussed above inrelation to FIG. 1A, the gate voltage is instead applied between thegate electrode 4 and the source contact 1. There is no difference inpotential between the positions for the negative polarity of the V_(g)voltage, but the change of this position makes it possible toshort-circuit the gate electrode and source contact through replacingV_(g) with a conductor. Such a short-circuit results in that, when apositive voltage is applied to the source contact 1, the gate electrode4 will be polarized positively also. Accordingly, and as describedabove, resistance will mount within the transistor channel uponreduction or oxidation in the electrochemically active element 3, whichresistance will hinder charge transport there through. As the resistancein the channel mounts, the current supplied to the “common” source andgate will increasingly be led to the gate electrode, further feeding theelectrochemical reaction and thus raising the resistance in thetransistor channel even more. If the polarity of the source-drainvoltage is reversed, the opposite situation will arise, so that theelectrochemically active element is instead rendered conducting. Thus,the device, when the source and gate are connected in this way, willallow current in one direction and not in the other, and in practicefunctions as a diode.

The diode is operative as long as there is a voltage applied between the“common” source electrode 1 and the separate gate electrode 4. However,short-circuiting the common electrode 1 and the gate electrode 4 will inprinciple give the same result as an applied voltage. In other words, adiode functionality is provided even if the gate voltage V_(g) is set at0 V.

Dynamic transistor: FIGS. 2A and 2B schematically show a dynamictransistor. The transistor comprises a source contact 1, a drain contact2 and an electrochemically active element 3, which have all been formedfrom a continuous piece of organic material. The electrochemicallyactive element 3 comprises a transistor channel 3 a and a redox sinkvolume 3 b. Both the source and drain contacts are in electrical contactwith an external power source, which allows the application of a voltageV_(ds) between them. The transistor further comprises two gateelectrodes 4 a and 4 b arranged on either side of the electrochemicallyactive element 3. The gate electrodes can be formed from the sameorganic material as the source and drain contacts and theelectrochemically active element. The gate electrodes are in electricalcontact with an external power source, which allows application of avoltage V_(g) between them. All of these organic material componentshave been deposited in one layer on a support 6. On top of this layer,covering parts of the gate electrodes 4 a and 4 b and the active element3, is a layer of gel electrolyte 5. Furthermore, the gel electrolytelayer 5 is covered with an encapsulating layer 7 for prevention ofsolvent evaporation.

Working principle for the polarity of V_(g) shown in FIG. 2, and in thecase of an organic material which is conducting in its oxidized stateand non-conducting when reduced to its neutral state: when a gatevoltage V_(g) is applied between the gate electrodes 4 a and 4 b, gateelectrode 4 a is polarized positive (anode), and gate electrode 4 b ispolarized negative (cathode). This leads to onset of electrochemistry inthe electrochemically active element; the organic material in thetransistor channel 3 a (adjacent to gate electrode 4 a) is reduced,while the organic material in the redox sink volume 3 b (adjacent togate electrode 4 b) is oxidized. These electrochemical reactions requirean internal transfer of electrons within the electrochemically activeelement. Electrons that are released in the oxidation reaction in theredox sink volume migrate to the transistor channel, where theyreplenish the electrons consumed in the reduction of organic materialoccurring in this segment of the electrochemically active element. Thereduced volume in the transistor channel displays a drasticallydiminished electrical conductivity, which results in the closure of thetransistor channel and an effective reduction of the source-draincurrent for a given source drain voltage V_(ds), i e the transistor is“off”. When the external circuit applying voltage to the gate electrodes4 a and 4 b is broken, a spontaneous discharge occurs, in that electronsflow from the reduced material in the transistor channel to the oxidizedmaterial in the redox sink volume, until the original redox state isre-established within the electrochemically active element. Formaintenance of overall charge neutrality, this flow of electrons withinthe electrochemically active element is accompanied by an ion flowwithin the solidified electrolyte.

Bi-stable transistor (type 2): FIGS. 3A and 3B schematically showanother embodiment of a bi-stable transistor, the architecture of whichis based on the dynamic transistor architecture described immediatelyabove. With reference to FIGS. 3A and 3B, this embodiment of a bi-stabletransistor has the same components as said dynamic transistor, thedifference being that the layer of solidified electrolyte 5 ispatterned, forming two separate segments of electrolyte 5 a and 5 b.This patterning has the effect of interrupting ion flow within theelectrolyte, which interruption in turn means that no spontaneousreversal of electrochemical reactions can occur between transistorchannel 3 a and redox sink volume 3 b. In similarity to the case of thefirst bi-stable transistor device described above, the oxidation stateof the transistor channel is maintained when the external circuit, heresupplying voltage to the gate electrodes, is broken.

Experiment 1 (on Bi-stable and Dynamic Transistors)—Materials andMethods

Bi-stable (type 1) and dynamic transistors were realized by patterningfilms of partially oxidized poly(3,4-ethylenedioxythiophene) withpoly(styrene sulphonate) as counterions (frequently referred to asPEDOT:PSS in the present text) into a T-shaped structure. The designfollowed the schematic drawings of the bi-stable and dynamic transistorspresented in FIGS. 1 and 2, respectively. In its pristine, partiallyoxidized state, PEDOT:PSS films as provided in the form of ORGACON™EL350 from AGFA are conductive, providing the opportunity of modulatingthe current in the transistor channel by reduction of the PEDOT:PSSelectrochemically. All processing and material handling was done inambient atmosphere.

Patterning through screen-printing: PEDOT:PSS was applied as a thin filmon a polyester carrier, ORGACON™ EL-300Ω/ square, as provided by AGFA.Conducting patterns were generated using a screen-printed deactivationpaste: ORGACON-STRUPAS gel, as provided by AGFA, was mixed with anaqueous sodium hypochlorite solution, resulting in a concentration ofthe active degradation agent of approximately 1.2%. Printing wasperformed using a manual screen printing board (Movivis, purchased fromSchneidler) using a screen with 77 lines/cm mesh. After 1 minute, thedeactivation agent was removed from the PEDOT:PSS film by washingthoroughly with copious amounts of water.

Deposition of source and drain contacts and gate electrode(s): Afterpatterning of the PEDOT:PSS film, silver paste (DU PONT 5000 Conductor)was printed on top of the PEDOT:PSS areas that form the drain and sourcecontacts and gate electrode(s) in order to improve the electricalcontact of the respective element. Alternatively, the transistors can beentirely made of organic materials by locally increasing the layerthickness of the PEDOT:PSS in the gate, source and drain areas bydrying-in of a PEDOT-PSS solution (BAYTRON P™ from Bayer) onto theseareas. Such all-organic transistors were successfully realized onpolyester foils.

Deposition of gelled electrolyte: Calcium chloride (2%), iso-propanol(35%), and gelatin (10%) (Extraco gelatine powder 719-30) were dissolvedin de-ionized water at approximately 50° C. (weight percentages of theresulting gel in parenthesis). Structures of gelled electrolyte onpatterned PEDOT:PSS film were formed by printing the gel on top of thePEDOT:PSS film. The thickness of the gelled electrolyte ranged from 20to 100 μm. Gelled electrolyte structures were realized at line widthsdown to 300 μm. Screen-printing of gelled electrolyte was performedusing a 32 mesh screen. The distance between the drain and sourcecontacts was typically 1 to 2 mm.

Encapsulation: The gelled electrolyte was coated with a waterproofcoating, such as plastic paint or foils, encapsulating the device. Shelflifetimes of several months were achieved.

Electrical characterization: All testing was performed in ambientatmosphere at room temperature. Current-voltage (I-V) transistor curveswere measured with a HP Parameter Analyzer 4155 B, in combination withan external HP E3631A power supply.

Experiment 1—Results

Bi-stable transistor: A bi-stable transistor such as that shownschematically in FIGS. 1A and 1B was realized. The bi-stable transistorhad a transistor channel width of 600 μm and a gel width of 800 μm, witha transistor channel of 0.48 cm². However, smaller dimensions were alsosuccessfully tested using photolithographic photoresist patterning incombination with reactive ion plasma etching. These devices exhibitedchannel widths ranging from 5 to 20 μm and a gel width of 20 μm.

Typically, the gate voltages V_(g) applied to the gate electrode were inthe interval between 0 V and 0.7 V. Drain-source characteristics weredetermined by sweeping the source-drain voltage from 0 V to 2 V. Theresulting I-V curves are displayed in FIG. 4.

Characteristic switching times for the conductivity modulation weredetermined by applying a square shaped modulation voltage (alternatingbetween 0 V and 1 V) and measuring the resulting current changes.Typical rise and decline times (defined as the time required for a 90%increase respectively decrease of the current level) were determined as0.1 s and 0.2 s, respectively.

On/Off ratios (defined as the current ratio I_(ds,max)/I_(ds,min) at asource-drain voltage V_(ds) of 2 V for V_(g)=0 V (on) and V_(g)=0.7 V(off)) reached 15000. FIG. 4 displays the output characteristics of thebi-stable transistor, I_(ds) vs V_(ds) for different gate voltages.

The inset in FIG. 4 shows the source-drain current I_(ds) as a functionof the gate voltage V_(g) for a constant source-drain voltage V_(ds)(V_(ds)=2 V). From these curves, an important parameter, thetrans-conductance g_(m), can be evaluated. g_(m) is defined as:

$g_{m} = {\frac{\delta\; I_{ds}}{\delta\; V_{g}}\left( {V_{ds} = {constant}} \right)}$

The value of the trans-conductance of the bi-stable transistor devicewas found to be −1.2 mA/V.

Dynamic transistor: A dynamic transistor such as that shownschematically in FIGS. 2A and 2B was realized. The dynamic transistorhad a channel width of 250 μm and a gel width of 900 μm, with atransistor channel of 0.23 cm². However, smaller dimensions of PEDOT andgel patterns down to 4 μm were successfully reached usingphotolithographic patterning. These devices exhibited channel widthsranging from 4 to 20 μm and a gel width of 20 μm.

Typically, the gate voltages V_(g) applied to the gate electrodesspanned an interval of 0 V to 3 V. On/Off ratios (defined as the currentratio I_(ds,max)/I_(ds,min) at a source-drain voltage V_(ds) of 2 V forV_(g)=0 V (on) and V_(g)=3 V (off)) reached 1000. FIG. 5 displays theoutput characteristics of the dynamic transistor, I_(ds) vs V_(ds) fordifferent gate voltages.

The inset in FIG. 5 shows the source-drain current I_(ds) as a functionof the gate voltage V_(g) for a constant source-drain voltage V_(ds)(V_(ds)=2 V). From these curves, the value of the trans-conductance ofthe dynamic transistor device was found to be −0.10 mA/V.

Experiment 2 (On Bi-stable Transistors)—Materials and Methods

Bi-stable (type 1) transistors were realized by patterning films ofpolyaniline. The design followed the schematic drawing of the bi-stabletransistor presented in FIGS. 1A and 1B.

Patterning through evaporation and doctor blade: PANIPOL™ F (commercialpolyaniline) was provided in solution in toluene or in m-cresol, at aconcentration of 10 mg/ml in both cases. One transistor was madestarting from each of the two solutions of polyaniline. The solvent wasevaporated, and the polyaniline formed a thin film on a plastic carrier(conventional transparency films). Conducting patterns were made using adoctor blade.

Deposition of source and drain contacts and gate electrode: Afterpatterning of the polyaniline film, silver paste (DU PONT 5000Conductor) was printed on top of those polyaniline areas that formed thedrain and source contacts. To ensure good contact with the power source,a silver paste (DU PONT 5000 Conductor) was printed on to the areas notcovered with electrolyte on the gate electrode. Alternatively, thetransistors can be entirely made of organic materials by locallyincreasing the thickness of the layer of polyaniline in the gate, sourceand drain areas, by drying-in of a polyaniline solution (e g Panipol™)onto these areas.

Deposition of gelled electrolyte: In the transistor employingpolyaniline originally dissolved in toluene, gelatin (Extraco gelatinpowder 719-30) was dissolved in de-ionized water at approximately 50°C., in an amount resulting in a gel having 10% by weight of gelatin,which was used as electrolyte. In the transistor employing polyanilineoriginally dissolved in m-cresol, BLÅGEL™ (purchased fromApoteksbolaget, Sweden) was used as gelled electrolyte. Structures ofgelled electrolyte on the respective patterned polyaniline films wereformed by painting the gel on top of the polyaniline films with a brush.The thickness of the gelled electrolyte ranged from 100 to 300 μm. Thedistance between the drain and source contacts was typically from 1 to 2cm.

Electrical characterization: All testing was performed in ambientatmosphere at room temperature. Current-voltage (I-V) transistor curveswere measured with a HP Parameter Analyzer 4155 B in combination with anexternal HP E3631A power supply.

Experiment 2—Results

Bi-stable transistors such as that shown schematically in FIGS. 1A and1B were realized. The bi-stable transistors had a transistor channelwidth of 3 mm and a gel width of 4 mm, with a transistor channel of 12mm². Typically, the gate voltages V_(g) applied to the gate electrodewere in the interval between −15 V and 15 V. Drain-sourcecharacteristics were determined by sweeping the source-drain voltagefrom 0 V to 10 V. The resulting I-V curves are displayed in FIG. 6(polyaniline supplied in toluene solution) and FIG. 7 (polyanilinesupplied in m-cresol solution).

On/Off ratios (defined as the current ratio I_(ds,max)/I_(ds,min) at asource-drain voltage V_(ds) of 2 V for V_(g)=0 V (on) and V_(g)=4 V or−4 V (off)) reached 100 for both negative and positive gate voltages.

Three-terminal Transistors

Due to the impracticality to design circuits based on transistors withfloating gate supplies a three-terminal transistor having a fixed gatesupply will be described in the following. In this mode there is onlyone gate electrode and its potential is always referenced to the drainor source electrode. Thus, unlike the four-terminal devices describedabove and having 2 gate electrodes, three-terminal devices have only onegate electrode and the gate potential is thus fixed in relation to thesource/drain potentials. In comparison, the controlling gate potentialin four-terminal devices is applied over the two gate electrodes andthus floats with respect to drain and source.

3-terminal electrochemical transistors have been investigated from afunctional point-of-view. As it turns out, “normally open” transistors(i.e. transistors that close the transistor channel upon application ofa voltage to the gate electrode) have characteristics that are similarto p-channel depletion-mode mosfet devices. Many of the most promisingorganic materials for the present invention (e.g. PEDOT:PSS) result insuch “normally open” transistors, and electrical design rules for properoperation of such “normally open” electrochemical transistors havetherefore been established and are specified below.

An example of a three-terminal electrochemical transistor 900 isillustrated in FIG. 9 a (top view on left and side view on right). Theelectrochemically active element 901 comprises a thin channel 907 ofPEDOT:PSS on top of which electrolyte 902 is deposited. The electrolyte902 thus defines a transistor channel 903. The area of the transistorchannel may, for example, be 0.5*0.5 mm2, and the thickness may be 0.2μm (for example using ORGACON™ EL350 foil from AGFA). The electrolyte902 is extended over the gate electrode 904 so that it covers a muchlarger area than on the transistor channel side to avoid over-oxidizingthe gate electrode. The larger areas of the three terminals (i.e. thegate electrode 904, the source contact 905, and the drain contact 906)are used as “pad areas” to allow easy connection to the device.

The thin parts 907 of the electrochemically active element that extendoutside the transistor channel are kept to a minimum in order tominimize the on-resistance of the transistor. However, the existence ofsuch parts 907 is advantageous for two reasons. First, they allow somemis-alignment of the electrolyte. The second reason is that thetransistor channel reduction has a tendency to migrate somewhat outsidethe electrolyte-covered area. In order to limit the buildup ofpermanently reduced areas, this spreading process should be as confinedas possible. To this end, each of the two extended portions 907 may haveabout the same size as the electrolyte-covered part of the transistorchannel. Using PEDOT:PSS as organic material, and the dimensions givenabove, each of these extended portions show a resistance of about 1kohm.

The structure illustrated in FIG. 9 a is an example of a lateraltransistor. As stated above, it is alternatively possible to use avertical design, rendering vertical transistors having the gateelectrode positioned on-top of the channel. The fundamental differencesbetween vertical and lateral devices are illustrated in FIG. 8 (top viewon left and side view on right). In the vertical configuration the gateelectrode 803 is sandwiched on the transistor channel 804, having theelectrolyte 805 as an intermediate carrier, and the source and drainelectrodes 801, 802 are typically arranged in the same plane as thetransistor channel 840. Obviously, vertical as well as lateralconfigurations may be employed for any type of transistor that is inaccordance with the present invention, and not only for thethree-terminal transistor.

In general, vertical transistors enable faster injection of ions intothe transistor channel. However, apart from an increased speed, the twostructures show similar electrical performance. FIG. 9 b compares theperformance of vertical and lateral transistors. The transistors areset-up as shown in FIG. 10 and described below as the third quadranttest. The drain-source current is measured for an input signal whichtoggles between 0 and 1 volts. Up to two orders of magnitude fasterswitching speed has been noticed in vertical transistors compared tolateral transistors. In real circuits such as the logical gatesdescribed above, this translates into less than a second switching timeas compared to about 10 seconds for the lateral-based circuits.

The temporal response of the transistor may be improved if a verticalconfiguration is employed. However, vertical structures generallyrequire an additional layer of conducting material. On the other hand,when implementing more complex circuits consisting of many gates themanufacturing process must anyway allow for at least a second layer ofconnecting wires. This will most often open up the possibility toproduce vertical transistors without additional manufacturing steps.

Experiment 3 (On Three-terminal Transistors)—Materials and Methods

PEDOT:PSS was used as electrochemically active organic material. ThePEDOT:PSS was coated on a polyester carrier as supplied by AGFA underthe trade name ORGACON™ EL350. As electrolytes, two different mixtureswere used. One was a mixture of hydroxyethyl-cellulose, sodium citrate,glycerol and DI-water, the other was a mixture of PSSNa, D-sorbitol,glycerol and DI-water.

The circuits presented were manufactured with a standard large areaplotter (FC 2200, supplied by GraphTech Corporation). Patterns werecreated in the PEDOT:PSS film by mounting a knife in the pen holder. Byapplying a force just strong enough to cut through the PEDOT:PSS layer,but not through the polyester foil, different patterns were created. Inorder to define the area for the electrolyte, openings were created in alamination foil which was laminated onto the PEDOT:PSS film. Theelectrolyte was drop caste in the opening followed by a baking step, 60°C. for 10 minutes. The resulting devices were thus not dependent on anynarrow lines or thin dielectrics. In combination with solubility incommon solvents this approach thus enables large-scale manufacturingusing common printing techniques.

All measurements were performed in ambient atmosphere. Measurements areperformed with Keithley 2400 Sourcemeter and HP power supply E3621Acontrolled via Labview.

Results

In case the transistor typically is symmetric, there is no way todistinguish a priori between the source and drain. Rather, this will bea function of the applied voltages. Two test configurations will bedistinguished in the following, depending on whether the gate voltage isreferenced to the negative drain/source-supply or to the positivedrain/source-supply. These configurations are referred to as firstquadrant test circuit and third quadrant test circuit, respectively(left and right in FIG. 10, respectively). In FIG. 10 a transistorsymbol 1001 that resembles a conventional transistor but still pointsout the particular structure of the electrochemical device is suggested.

Measured characteristics in the first quadrant case (left in FIG. 10) isshown in FIG. 11. The graphs show the current through the transistordevice as a function of the drain/source voltage parameterized by theapplied gate voltage. The bottom graph thus relates to a gate voltage of1.0 V, and the top graph relates to a gate voltage of 0.0 V. With 0.0 Vat the gate, the transistor has a purely resistive behavior. Itson-resistance is seen to be about 4 kohm. If the gate voltage isdecreased into negative values (not shown in the graph) the channel willoxidize further. However, since the PEDOT:PSS material is alreadyoxidized to about 80% in its “natural state” (as supplied by AGFA) itsresistance will only decrease very slightly. Also, there is a strongrisk of the channel getting over-oxidized (rendering permanentlynon-conductive). Instead, increasing the gate voltage is moreinteresting as this starts to reduce the channel raising its resistanceand thus lowering the current. The net effect is that the gate voltagemodulates the drain/source current. By careful inspection it can be seenthat the gate voltage has the strongest impact when it is larger thanthe drain/source voltage. As the drain/source voltage increases beyondthe gate voltage the (differential) resistance will approachapproximately the same level (4 kohm), independent of the applied gatevoltage. Comparing to earlier known electronic devices, the I-V curvesbear some similarities with those of triode vacuum tubes.

The characteristics in the third quadrant show entirely differentbehavior as seen in FIG. 12. Rather than a resistive behavior the deviceenters into a constant-current mode as the voltage across it isincreased. The gate voltage now controls the level of the current. Suchbehavior is well-known from traditional semiconductor and vacuum tubedevices. In fact the similarity between our transistor and the pentodetube is quite strong. Both devices require the control potential to beoutside the range of the voltage across the device. In the pentode case,the (grid) control voltage is negative while the applied (anode/cathode)voltage is positive. For our transistor the same is true but withreversed polarities. Also, for the pentode, too high positive gridvoltage may destroy the device as this will lead to high grid currents.This is in analogy with the fact that negative voltages on the gateelectrode may ruin the electrochemical transistor due to over-oxidation.Hence, it is realized that the three-terminal “normally open”electrochemical transistor has similarities with certain traditionalelectronic components.

Comparing with semiconductor devices, most of them are of theenhancement type where conduction is increased with increased controlvoltage. In fact, the behavior of the “normally open” electrochemicaltransistor is better recognized as a depletion mode transistor. Inparticular, a p-channel depletion mos-fet transistor can be used as agood model for our 3-terminal transistor. FIG. 13 shows thecharacteristics of such a transistor from a SPICE simulation (SimulationProgram with Integrated Circuit Emphasis) where the geometry and dopingparameters have been adjusted to give comparable voltage and currentlevels with our electrochemical transistor.

A closer investigation of the two “modes” of operation shows thatthird-quadrant (pentode-style) mode is superior to first-quadrant mode.This can be seen by trying to fit “load-lines” to the characteristicsshown in FIGS. 11 and 12 for a conceptual single-stage amplifier. It ishardly possible to achieve amplification at all in the first quadrantwhile this is easy to achieve in the third quadrant. Thus, all circuitdesigns to be described here utilize the transistor in thethird-quadrant mode (corresponding to “normally open” mode).Furthermore, as was pointed out earlier, additional complexity isintroduced in the circuitry design since the range of the input (gate)and output (source/drain) voltages do not overlap each other.

Given this background, using PEDOT:PSS in the form of ORGACON™ EL350foil, we can now formulate three basic rules for the three-terminaltransistor:

-   -   The source/drain terminal that is connected to the highest        voltage defines the source.    -   Active behavior (switching, modulation) is obtained when gate        voltage is higher than source voltage.    -   Gate voltage must never become lower than the drain voltage in        order to avoid over-oxidation. Or, to be more specific: the gate        voltage should never become more negative than the most negative        potential in the channel of the transistor. Usually the most        negative potential is defined by the drain voltage but it is        possible, if the gate voltage changes rapidly, that part of the        channel may over-oxidize due to dynamical effects. A more        conservative rule that is always safe is thus to avoid that the        gate voltage decreases below the source voltage.

However, alternative measures may be taken in order to reduce theoccurrence of over-oxidation in the polymer. Such measures include, forexample, the addition of additives to the electrolyte, and hencefacilitate more liberal design rules.

Furthermore, we can use a suitably modified electronic model of thep-channel mos-feet device to mimic the behavior of our transistor. Forour test transistor this amounted to selecting a silicon device with achannel length of 1 μm and width 3 μm. In the SPICE simulator,“Threshold” was set to 1 volt, “transconductance” was set to 10⁻⁴, anddrain and source “ohmic resistance” was set to 1 kohm, respectively.

Viewed as a p-channel device, we can now construct a single stageamplifier 1400 or switch as shown in FIG. 14. The amplifier 1400comprises an electrochemical transistor 1401 and a resistor 1402. A lowinput will keep the transistor in a conducting state and the output willapproach the supply voltage. How close it will get depends on the ratiobetween the load resistor and the remaining transistor resistance. FIG.15 shows the input/output relation (transfer function) for a supplyvoltage of 2 V. As is seen, the input has to be above this level beforewe reach a suitable working point. This is in accordance with the seconddesign rule above. The small-signal (differential) amplification reachesvalues of about 10 for R=100 kohm. There is a hysteresis effect due tothe difficulties of reoxidizing the transistor channel, once it has beenreduced. However, some of this behavior is dynamic in the sense thatlowering the sweep rate of the input voltage will yield a smallerhysteresis and a slow enough measurement is likely to eliminate thehysteresis altogether.

As the drain terminal reaches a potential close to the supply voltagesimultaneously with a low gate voltage there is an obvious risk forover-oxidation of the transistor channel. In fact, the measured circuitsdid not allow the gate voltage to approach 0 volt before they becamedestroyed. Thus, to avoid this to happen, a fixed offset added to theinput signal is needed. This can either be achieved through a separatebattery, an additional circuitry or by chemical means.

Circuitries

In the following, a number of exemplifying circuitries will bedescribed.

Constant Current Source

FIG. 16 shows how a constant current source 1600 can be constructedbased on a three-terminal transistor. The circuitry comprises anelectrochemical transistor 1601, a resistor 1602, and a load resistor1603. This circuit utilizes the fact that the I-V curves are essentiallyhorizontal in the third quadrant. Thus, as long as the working point ofthe circuit lies on such a horizontal path, the current through the loadwill remain the same, independent on the value of the load resistorR_(L) and the supply voltage V.

It is now possible to design an inverter through the use of the constantcurrent source. This is achieved by connecting a load resistor 1701 (R3)in series with the input signal. The complete circuit is shown in FIG.17, and further comprises a first transistor 1702, a first resistor1703, a second transistor 1704, and a second resistor 1705. Physically,the circuit is implemented by cutting out PEDOT “islands” with a knifeas described earlier. Resistors were made by slicing the PEDOT into thinserpentine “wires”. The resistor values in this particular embodimentwere selected as follows, R1=64 kΩ, R2=16 kΩ and R3=32 kΩ and the supplyvoltages are V2=3.5 V, V3=1 V. The corresponding physical layout isshown in FIG. 18, where the resistors are arranged as “S-curved”resistor paths.

The transfer function for the inverter illustrated in FIGS. 17 and 18 isgiven in FIG. 19. The differential gain is not as large as for thecircuit in FIG. 16. The reason for this is that the value of R1 as wellas the applied voltage over the switching transistor is lower comparedto FIG. 16. Apart from being operative as an amplifier for small signals(centered around 0.5 volts) we can also use this device as a logicalinverter. An input in the interval 0-0.2 volt (logical 0) will give anout put of 0.8 volt (logical 1) while an input of 0.8 volt or above willyield an output of 0.2 volt.

FIG. 20 shows the behavior for a “binary” input signal. The graph showsthe input voltage (2001, V_(in)) and the corresponding output signal(2002, V_(out)). However, this particular circuit may not be the optimalchoice as a basis for logic circuitry. A potential problem is that theinput impedance is low. In fact a detailed analysis will show that the“fan-out” may even be lower than 1, meaning that this circuit would notbe able to drive a similar circuit. Thus, new designs may be necessaryto achieve reliable logical functions. Such new design will be describedin the following.

Single Stage Logical Inverter

FIG. 21 proposes a circuit 2100 for a single stage logical inverter. Theinput is directly connected to the transistor gate which leads to highinput impedance. The transistor (T₂) is biased to work in the thirdquadrant and generates the basic inverted signal on its drain terminal.A resistor network shifts the output signal back to the interval [0,1]used to represent the logical levels. When 1 volt is applied to thegate, the transistor (T₂) is shut-off and the output level is defined byvoltage division between the three resistors (R, R₀, and R₁) connectedin series. For a 0 volt input the transistor (T₂) is switched oneffectively reducing the resistor network to only include the two topresistors (R and R₀), now connected to ground rather than to thenegative supply. The circuit requires two supply voltages (V and V₁). Byproper selection of resistor values the supply voltages can be chosen tobe symmetric with regard to ground. Through simulations and practicalevaluation has been found that V₁=V=3 volt is a suitable voltage levelfor this circuit, and that suitable resistor values are R=80 kΩ, R₀=50kΩ, R₁=20 kΩ.

FIG. 22 shows the transfer function for circuitry 2100. The upper andlower curves represent stepping-up and a stepping-down of the inputvoltage, respectively. This hysteresis depends to a certain degree onthe sweep rate of the measuring equipment.

The temporal behavior of circuitry 2100 is illustrated in FIG. 23.Similar to what can be seen in FIG. 20, the leading edges are slowerthan the falling edges. This is due to a general property of theelectrochemical transistor, namely that turn-on is much slower thanturn-off. One explanation to this phenomena is that there is not astrong electric field that drives the reoxidation of the transistorchannel in contrast to the reduction of the channel that takes placewhen a positive voltage is applied to the gate. Another, relatedphenomena that is observed is that the reduction front which appears onthe drain side leaks a bit into the channel part that lies outside theelectrolyte. This reduced part of the transistor channel will remain inlow conductivity also after the rest of the channel has been reoxidizedleading to a gradual decrease in performance. This effect is discussedabove, and implies that the transistor channel should have a limitedcross-section towards the remainder of the electrochemically activeelement.

By combining the basic inverter stage with the current generatormentioned previously, a circuit can be achieved that will operate atsomewhat lower voltages than the single stage inverter (e.g. V=V1=2 V).Such a circuitry is shown in FIG. 24. The circuit uses the same twostages as the amplifier shown in FIG. 17 but in reversed order. Theresistances may be selected as, for example: R₁=17 kΩ, R₃=30 kΩ, R₄=20kΩ. The benefit is that the input impedance now becomes high and thatthe transfer function is somewhat steeper than for the single stageinverter as there is no resistive damping effect from the level shiftingstage.

Ring Oscillator

Employing a number of inverters it is possible to arrange a ringoscillator 2500. It consists of an odd number of inverters 2501connected to each other in a ring as shown in FIG. 25.

The minimum number of inverters to produce oscillation will depend onthe amplification and phase response of the individual inverters. Thering oscillator has been a classical circuit to generate clock signalsin simple digital systems. Its main use however has been for measuringthe switching speed of a semiconductor technology and this is usefulalso in our case. With five inverters of the single-stage type shown inFIG. 21, oscillation is stable and produces well-defined logical levels.FIG. 26 shows the output from one of the inverters, both on a short timescale (top) and on a longer timescale (bottom). One full period takesabout 100 s indicating that each stage has an average switching time ofabout 10 s. There is a slight decrease in frequency over a longer periodwhich is visible from the bottom curve. This is likely due to themigration of reduced PEDOT mentioned earlier that accumulates on thedrain side of the transistor channels.

Logical Gates

Logical gates such as NAND- and NOR-gates can be implemented as simpleextensions of the inverters, as illustrated in FIG. 27. By using twotransistors in parallel instead of the single input transistor, bothgates must be at a high potential to generate a low output value, thus a2-input logical NAND function 2701 is achieved. Likewise, transistors inseries will yield a NOR function 2702. Examples of input/outputrelations for the NAND and the NOR gate are shown in FIGS. 28 and 29,respectively, and relate to circuits where R1=20 kΩ, R0=50 kΩ, and R=70kΩ. The NAND gate has a fall time T_(f)=0.5 s and arise time T_(r)=1.44s, and the NOR gate has a fall time T_(f)=0.1 s and a rise time T_(r)=2s. It can be observed that the non-symmetry in turn-off versus turn-ontime for the transistors are particularly exaggerated in the case of theNOR-gate (FIG. 29). These measurements are performed on the circuitsillustrated in FIG. 27 and based on transistors having a verticalconfiguration. In fact, the shorter overall times for these twoparticular circuits are due to the use of vertical transistors insteadof lateral transistors in the.

Obviously, AND and OR gates are readily provided, for example, by addingan inverter to a NAND or NOR gate, respectively.

Analogue Amplifier

An example of an analogue circuit is given in FIG. 30 (left), in theform of a basic analogue amplifier. The circuit comprises a transistorM0, a constant current source IVm, and a resistance R at 20 kΩ. Theconstant current source may, for example be designed as described abovewith reference to FIG. 16. That particular constant current source 1600may be used also in the circuitries described below where such acomponent is needed.

On right, graphs showing the response modulated in SPICE is given, theupper graph relates to the input voltage (V_(in)), and the lower graphrelates to the output voltage (V0).

Single Stage AC-bypassed Amplifier

Another analogue circuit is illustrated in FIG. 31 (left), in the formof a single stage AC-bypassed amplifier. The circuit comprises atransistor M0, two resistors (R at 200 kΩ and R0 at 65 kΩ), a constantcurrent generator IVm, and a capacitor C=1 uF. The capacitor may beformed out of organic material as well, for example in line with theteachings in the article “All-polymer RC filter circuits fabricated withinkjet printing technology”, Chen at el, Solid-State Electronics 47(2003) 841-847.

On right, graphs showing the response modulated in SPICE is given. Theupper graph relates to the input voltage (V_(in)), and the lower graphrelates to the output voltage (V0).

Differential Amplifier

FIG. 32 a illustrates a differential amplifier that comprises twotransistors M and M0; three resistors R=120 kΩ, R0=120 kΩ, and R1=20 kΩ;a constant current source IVm0; and a feed voltage V1=3 V.

FIG. 32 b illustrates the AC characteristics of the differentialamplifier. The graph having the highest amplitude is, of course, thevoltage response and the other graph represents the input voltage.

FIG. 32 c illustrates the DC characteristics of the differentialamplifier. The slowly increasing graph relates to the input voltage andthe more rapidly decreasing graph relates to the output voltage.

“High Gain” Amplifier

FIG. 33 a illustrates a “high gain” amplifier, comprising two resistorsR=R0=10 kΩ, two transistors M and M0, and a constant current source IVm.

FIG. 33 b illustrates the response of the “high gain” amplifier, inputvoltage versus output voltage. The amplifier exhibits a clearstep-function at an input of 0 V.

Drivers

Various high fan-out drive circuits can also be provided. High fan-outdrive circuits are useful e.g. for providing clock signals. Someexamples of high fan-out drivers are given below.

FIG. 34 a, for example, illustrates a power inverter that comprisesthree resistors R=80 kΩ, R0=10 kΩ, and R1=15 kΩ; two transistors M andM1, a constant current source IVm; and a feed voltage V=3 V. FIG. 34 billustrates output versus input voltages for the inverter.

FIG. 35 a illustrates a “high gain” inverter that comprises fourresistors R=80 kΩ, R0=30 kΩ, R1=45 kΩ, and R2=50 kΩ; three transistorsM, M0, and M1; a constant current source IVm; and a feed voltage V=3 V.FIG. 35 b illustrates input versus output voltages for the “high gain”inverter.

It is also possible to design pixel drivers for use in displays. Suchdriver must be capable of translating logic levels to appropriate signallevels. For example, electrochromic display cells typically need atleast 0.8-1 V swing (i.e. the voltage needed across the pixel cell tomake it change appearance). FIG. 36 a illustrates one possible pixeldriver that comprises one resistor R=30 kΩ, one transistor M0, and oneconstant current source IVm. The response of this circuit is illustratedin FIG. 36 b. An alternative pixel driver is illustrated in FIG. 37 a,and comprises two resistors R=1000 kΩ and R0=18 kΩ; two transistors Mand M0; one constant current source IVm; and a feed voltage V=3 V. Theresponse from this somewhat more complex pixel driver is illustrated inFIG. 37 b, where the output voltage is plotted as a function of theinput voltage.

FIG. 38 a illustrates a high voltage driver that comprises one resistorR=200 kΩ, one transistor M0, and one constant current source IVm. Thisdriver is capable of providing a substantially higher drive voltage, asis seen from the graph of FIG. 38 b. An input voltage ranging between −1V and 1 V gives an output voltage ranging between 0 V and ≈−46 V.

In addition, circuits including for example sensors, batteries,capacitors, and display elements may be provided. In essence, it hasbeen found that the electrochemical transistor can be used in circuitssimilar to those of as ordinary solid-state transistors as long as theparticular biasing required by the electrochemical transistor is takeninto account.

1. An electrochemical transistor device comprising: a flexiblesubstrate; a layer of organic material arranged on said substrate, whichmaterial has the ability to electrochemically alter its electricalconductivity through change of redox state thereof, said layer includesa source portion, a drain portion and a transistor channel portion; alayer forming a first gate electrode arranged on said substrate to theside of, and separated from, said layer of organic material; and a layerof solidified electrolyte arranged in overlapping electric contact withsaid first gate electrode and in overlapping electric contact only withthe transistor channel portion of said layer of organic material,thereby defining said transistor channel portion, such that currentbetween said source portion and drain portion is controllable by meansof a potential applied to said first gate electrode.
 2. A deviceaccording to claim 1, wherein a surface of said layer of organicmaterial facing said electrolyte comprises a transistor channel area,which is covered by said electrolyte, a source area and a drain area,which are devoid of said electrolyte, wherein said transistor channelarea is arranged between said source area and said drain area.
 3. Adevice according to claim 2, wherein said electrolyte extends acrosssaid layer of organic material.
 4. A device according to claim 1,wherein said layer of organic material and said electrolyte each areband shaped, and arranged crosswise relative each other, and wherein asurface of said layer of organic material facing said electrolytecomprises a transistor channel area, which is covered by saidelectrolyte, a source area and a drain area, which are devoid of saidelectrolyte, wherein said transistor channel area is arranged betweensaid source area and said drain area.
 5. A device according to claim 4,further comprising a second gate electrode, which is arranged on saidsubstrate in electric contact with said electrolyte and to the side of,and separated form, said layer of organic material such that said layerof organic material is arranged between said first gate electrode andsaid second gate electrode, and said band shaped electrolyte extendsfrom said first gate electrode across said layer of organic material tosaid second gate electrode.
 6. A device according to claim 1, furthercomprising a first layer and a second layer of ion isolative material,which layers are arranged between said layer of organic material andsaid electrolyte, said first layer covers an area between saidtransistor channel portion and said source portion of said layer oforganic material, and said second layer covers an area between saidtransistor channel portion and said drain portion of said layer oforganic material, wherein said first and second layers extend furtherthan said electrolyte from said transistor channel portion towards saidsource portion and said drain portion, respectively.
 7. A deviceaccording to claim 1, further comprising an ion isolative materialhaving an open area wherein the transistor is to be arranged, whereinthe ion isolative material is arranged between said solidifiedelectrolyte and said layer of organic material, such that less precisionis required when arranging said electrolyte relative to said organicmaterial.
 8. A device according to claim 1, wherein said layer oforganic material is further arranged to form a source electrode and adrain electrode, which extends from said source portion and said drainportion, respectively, of said layer of organic material.
 9. A deviceaccording to claim 1, wherein a source electrode and a drain electrodeare electrically connected to said source portion and said drainportion, respectively, of said layer of organic material.
 10. A deviceaccording to claim 1, wherein said first gate electrode and said layerof organic material are formed by means of printing.
 11. A deviceaccording to claim 1, wherein said layer of organic material and saidfirst gate electrode are arranged between said substrate and saidelectrolyte.
 12. A device according to claim 1, wherein said electrolyteis in direct electrical contact with said first gate electrode and saidtransistor channel portion of said layer of organic material.
 13. Adevice according to claim 1 wherein said current is controllable bymeans of a voltage applied across said first gate electrode and one ofsaid source portion and said drain portion of said layer of organicmaterial.
 14. A device according to claim 1, wherein said first gateelectrode is made of organic material.
 15. A device according to claim1, wherein said organic material is a polymer selected form the groupconsisting of polythiophenes, polypyrroles, polyanilines,polyisothianaphtalenes, polyphenylene vinylenes and copolymers thereof.16. A device according to claim 1, in which said organic materialfurther comprises a polyanion compound, the polyanion compound beingpoly(styrene sulphonic acid) or a salt thereof.
 17. A device accordingto claim 1, in which said solidified electrolyte comprises a binder. 18.A device according to claim 17, in which said binder is a gelling agentselected from the group consisting of gelatin, a gelatin derivative,polyacrylic acid, polymethacrylic acid, poly(vinylpyrrolidone),polysaccharides, polyacrylamides, polyurethanes, polypropylene oxides,polyethylene oxides, poly(styrene sulphonic acid) and poly(vinylalcohol), and salts and copolymers thereof.
 19. A device according toclaim 1, in which said solidified electrolyte comprises an ionic salt.20. A device according to claim 1, in which said flexible substrate isselected from the group consisting of polyethylene terephthalate,polyethylene naphthalene dicarboxylate, polyethylene, polypropylene,polycarbonate, paper, coated paper, resin-coated paper, paper laminates,paperboard, corrugated board and glass.
 21. An electrochemicaltransistor device comprising: a flexible substrate; a layer of organicmaterial arranged on said substrate, which material has the ability toelectrochemically alter its electrical conductivity through change ofredox state thereof, said layer of organic material comprising a sourceportion, a drain portion and a transistor channel portion; a layer ofsolidified electrolyte arranged in electric contact with said layer oforganic material at said transistor channel portion, thereby definingsaid transistor channel portion, and a gate electrode arranged inelectric contact with said solidified electrolyte, wherein saidelectrolyte is arranged in a sandwich structure between said layer oforganic material and said gate electrode such that current between saidsource portion and drain portion is controllable by means of a potentialapplied to said gate electrode.
 22. A device according to claim 21,wherein said electrolyte extends across said layer of organic material.23. A device according to claim 2, wherein a surface of said layer oforganic material facing said electrolyte comprises a transistor channelarea, which is covered by said electrolyte, a source area and a drainarea, which are devoid of said electrolyte, wherein said transistorchannel area is arranged between said source area and said drain area.24. A device according to claim 21, further comprising a first layer anda second layer of ion isolative material, which layers are arrangedbetween said layer of organic material and said electrolyte, said firstlayer covers an area between said transistor channel portion and saidsource portion of said layer of organic material, and said second layercovers an area between said transistor channel portion and said drainportion of said layer of organic material, wherein said first and secondlayers extend further than said electrolyte from said transistor channelportion towards said source portion and said drain portion,respectively.
 25. A device according to claim 21, further comprising astopping material being electrically conductive and ionicallynon-conductive, wherein the stopping material is arranged between saidsolidified electrolyte and said layer of organic material in order todelimit said transistor channel area from surrounding portions of saidlayer of organic material.
 26. A device according to claim 21, whereinsaid layer of organic material is further arranged to form a sourceelectrode and a drain electrode, which extends from said source portionand said drain portion, respectively, of said layer of organic material.27. A device according to claim 21, wherein a source electrode and adrain electrode is electrically connected to said source portion and adrain portion, respectively, of said layer of organic material.
 28. Adevice according to claim 21, wherein said gate electrode and said layerof organic material is formed by means of printing.
 29. A deviceaccording to claim 21, wherein said electrolyte is in direct electricalcontact with said gate electrode and said transistor channel portion ofsaid layer of organic material.
 30. A device according to claim 21,wherein said current is controllable by means of a voltage appliedacross said gate electrode and one of said source portion and said drainportion of said layer of organic material.
 31. A device according toclaim 21, wherein said gate electrode is made of organic material.
 32. Adevice according to claim 21, wherein said organic material is apolymer, and preferably a polymer selected form the group consisting ofpolythiophenes, polypyrroles, polyanilines, polyisothianaphtalenes,polyphenylene vinylenes and copolymers thereof.
 33. A device accordingto claim 21, in which said organic material further comprises apolyanion compound, the polyanion compound being poly(styrene sulphonicacid) or a salt thereof.
 34. A device according to claim 21, in whichsaid solidified electrolyte comprises a binder.
 35. A device accordingto claim 21, in which said solidified electrolyte comprises an ionicsalt.
 36. A device according to claim 21, in which said flexiblesubstrate is selected from the group consisting of polyethyleneterephthalate, polyethylene naphthalene dicarboxylate, polyethylene,polypropylene, polycarbonate, paper, coated paper, resin-coated paper,paper laminates, paperboard, corrugated board and glass.